Emissions arising from automotive exhaust have been a problem for several decades and approaches for addressing this problem have included the use of unleaded fuel (i.e., to control lead emissions arising from leaded fuels), oxygenated fuel (i.e., to reduce hydrocarbon emissions), and catalytic converters (i.e., to reduce hydrocarbon emissions).
Catalytic converters are now universally employed with gasoline and diesel powered vehicles and the efficiency of these converters is directly related to the ability of the catalyst to effectively convert un-burnt or partially burnt hydrocarbons generated during combustion to carbon dioxide and water. One problem arising with the use of such converters is poisoning of the catalyst, which results in reduced catalyst efficiency. Since catalytic converters are intended for extended use, catalyst poisoning results in higher levels of atmospheric discharges of pollutants from internal combustion engines over prolonged periods of time.
In order to minimize such poisoning, the automobile and truck industry has set standards for the concentrations of additives in both fuels and lubricants. With regard to the lubricants, one additive family currently addressed by industry standards is the phosphorus-containing additive family used in lubricant compositions employed to lubricate internal combustion engines. Specifically, phosphorus-containing additives reach the catalytic converter as a result of, for example, exhaust gas recirculation and/or blow-by processes as well as other methods that are well known in the art. In any event, phosphorus is known to accumulate in the catalytic converter and at active metal sites, thus reducing catalyst efficiency and effectively, over time, poisoning the catalyst and increasing hydrocarbon emissions. As a result of the above, the American Society for Testing and Materials (ASTM) has proposed new specifications (PC-10) that set the limitations of sulfated ash (no more than 1.0 wt %), phosphorus (no more than 0.12 wt %) and sulfur (no more than 0.4 wt %) in a heavy duty diesel engine oil.
A problem arises when the level of phosphorus is reduced in a lubricating oil composition containing an oil-soluble, phosphorus-containing, antiwear compound in that there is a significant reduction in anti-wear, anti-oxidation, and anti-corrosion performance arising from the decrease in the concentration of phosphorus in the engine oil.
This invention is directed to the discovery that heavy duty diesel engine oils comprising a major amount of an oil of lubricating viscosity and a borated alkaline earth metal sulfonate detergent, wherein the engine oil contains no more than 0.12 wt % phosphorus and no more than 1.25 wt % sulfated ash, reduces corrosion and decreases catalyst poisoning. This present invention meets the ASTM specifications for phosphorus, decreases hydrocarbon emissions and controls bearing lead corrosion.